Spinonema spirale, Larrazábal-Filho & Neres & Silva & Esteves, 2019

Larrazábal-Filho, Alexandre L., Neres, Patrícia F., Silva, Maria Cristina Da & Esteves, André M., 2019, A new genus with three new species of free-living marine nematodes of the subfamily Desmodorinae (Nematoda: Desmodoridae), from the continental shelf off northeastern Brazil, Zootaxa 4615 (2), pp. 321-342 : 330-334

Spinonema spirale gen. et sp. n.

( Table 2, Figures 6–8 ).

Type material: Holotype, Male adult, MNRJ 398 (04°45’00”S, 036°45’00”W) collected in June 2009 in the Po- tiguar Basin, between 30 and 45 m deep. Faciology: coarse lithoclastic sand. Gear: Van Veen /corer.

Paratype Female: Adult, MNRJ 399 (04°45’00”S, 036°45’00”W) collected in June 2009 in the Potiguar Ba- sin, between 30 and 45 m deep. Faciology: coarse lithoclastic sand. Gear: Van Veen /corer .

Other paratypes: 1 female (206 LMZOO-UFPE), 2 males (207-208 LMZOO-UFPE) and 4 juveniles. All juveniles in first stage of development (J1) (209 LMZOO-UFPE). Collected on same date as holotype. Juvenile stag- es were identified based on the developmental stage of the reproductive system, based on Bird and Bird (1991).

Etymology. Species name refers to the shape and turns of the fovea amphidialis.

Description. Holotype ( Figures 6 and 7 ). Body cylindrical, yellowish brown. Cuticle annulated, with vacuoles distributed irregularly, including base of cephalic capsule. The vacuoles are in the inner layer of the cuticle and not in its exterior Annulations absent on tail end with vacuoles. Cuticle with C-shaped lateral alae, thicker than rest of body ( Figure 6D ); alae begin 474 µm (445 and 482 µm for paratypes) from head. Annules are 4 µm wide in anterior region, 2 µm at midbody and 2.5 µm in posterior region. Somatic setae irregularly arranged or barely visible in pharyngeal region. Other somatic setae present along body, sparse and irregularly distributed. Dorsal spine strongly cuticularized, located on 9 th (8 th and 9 th for paratypes) cuticular ring, along the anterior half of pharyngeal region, and appearing as a projection of the cuticle ( Figures 6C and 7A ). Inversion of direction of cuticular annuli occurring after 63 rd (63 rd for all specimens) cuticular ring. Head square. Cephalic capsule 20 µm (27 and 28 µm for paratypes) long and well-developed, with thick cuticle without annulations. Anterior sensilla arrangement: six inner labial papilliform sensilla, six outer labial setiform sensilla. Four cephalic setiform sensilla positioned at anterior edge of fovea amphidialis. Subcephalic setae absent. Fovea amphidialis multispiral (3.15 turns for all specimens), occupying 72% (53% and 66% for paratypes) of diameter of head (smaller in female, i.e., sexual dimorphism). Oral cavity with one dorsal and one small ventral tooth. Pharynx cylindrical, with muscular pyriform endbulb. Nerve ring located posterior to middle of pharynx ( Figure 6F ). Ventral gland and secretory-excretory pore not observed. Cardia inserted in intestine. Reproductive system monorchic, with single anterior testis situated to left of intestine, outstretched. Sperm cells large, globular. Spicules short and arched, with proximal end rounded, and broad velum present. Gubernaculum intricate, with lateral crurae. Dorsal apophysis of gubernaculum wing-shaped. Cuneus surrounding distal portion of spicules ( Figure 5E ). Three caudal glands. Tail short, conical and with vacuoles. Spinneret present.

Paratype females ( Figures 7–8 ). Similar to male, with minor differences. Fovea amphidialis proportionally smaller, occupying 53% and 50% of cephalic capsule, and differing in number of turns (2.5 turns for all specimens; Figures 7C and 8A ). Another difference is in the position of the cephalic setae, which are located at the base of the cephalic capsule. Inversion of direction of annuli occurring after 58 th and 67 th cuticular ring. Lateral alae begin 292 and 279 µm from head. Nerve ring difficult to observe. Reproductive system with paired ovaries, opposite and reflexed. Both genital branches located to right of intestine. Vulva as simple transverse slit-like aperture. Vagina vera slightly cuticularized. Vagina uterina surrounded by constrictor muscle. No egg found in uterus. Vulva located at 39% and 38% of total body length from anterior end. Tail conical.

Juvenile ( Figures 7 and 8 ). Very similar to adults, except lacking lateral alae. However, the stage 1 juvenile has a distinctive characteristic, the presence of setae or spines on the cuticle ( Figures 7F and 8F ). In the course of further development, this feature is lost. Four juveniles were found, all in stage 1.

Diagnosis. Spinonema spirale gen. et sp. n. is characterized by having a cuticle with vacuoles in all parts of the body, a multispiral fovea amphidialis (3.15 turns), sexual dimorphism in the size of the fovea amphidialis and position of cephalic setae, one dorsal spine, lateral alae, gubernaculum intricate with a wing-shaped apophysis, surrounding the distal portion of the spicules.

Relationships Spinonema spirale gen. et sp. n. is similar to S. cuticulatum gen. et sp. n. The similarities are mainly in the cuticle, which shows strong annulations and vacuoles, a cuticularized dorsal spine and an inversion ring (structure that defines the inversion of the direction of the cuticular annuli). Differences also occur in the cuticle, i.e., in S. cuticulatum gen. et sp. n. the vacuoles start to appear from 9 th cuticular annule, whereas S. spirale gen. et sp. n. has vacuoles in all annules, including the cephalic capsule. The size, shape and number of turns of the fovea amphidialis differ between the two species: in S. cuticulatum gen. et sp. n. the fovea amphidialis has 1.25 turns, whereas in S. spirale gen. et sp. n. it has 3.15 turns (male) and 2.5 turns (female), with sexual dimorphism. However, the major differences are in the male reproductive system: in S. cuticulatum gen. et sp. n. the spicules have hook-shaped capitulum and the gubernaculum lacks an apophysis, whereas in S. spirale gen. et sp. n. the spicules have a rounded capitulum; the gubernaculum is intricate, with lateral crurae; the dorsal apophysis of the gubernaculum is wing-shaped; and the cuneus surrounds the distal portion of the spicules.

All juveniles found have similar characteristics to the adults. In this species, stage 1 juveniles have setae associated with cuticular annulations, which are lost during development. The presence of characters in juveniles that are later lost by adults has not been reported for any other species of Desmodorinae . However, this difference may only be apparent, because the descriptions of the majority of the species are inadequate and do not include descriptions of juveniles.

Figures

FIGURE 5. Spinonema cuticulatum gen. et sp. n. Paratype female MNRJ 397. A: overview; B and C: anterior region; D: ovary and vulva opening; G: tail region. E and F: juvenile in stage 1, anterior region.

FIGURE 6. Spinonema spirale gen. et sp. n. Holotype MNRJ 398. A: overview; B: tail region; C: anterior region; D: lateral alae (ANT anterior part and POS posterior part); E: spicules; F: anterior region; G: Inversion of direction of annuli.

FIGURE 7. Spinonema spirale gen. et sp. n. A and D, Holotype MNRJ 398; A: Cephalic region; D: Spicules. C and E, Paratype female MNRJ 399; C: Cephalic region; E: Tail region. B and F, Paratype juvenile in stage 1; B: Cephalic region; F: Spines on cuticle.

FIGURE 8. Spinonema spirale gen. et sp. n. Paratype female MNRJ 399. A and B: anterior region; C: overview; D: tail region; E: ovary and vulva opening. Paratype juvenile in stage 1. F: spines on cuticle; G: tail region; H: anterior region.